Three-piece, wound golf balls with balata covers are preferred by most expert golfers. These balls provide a combination of distance, high spin rate, and control that is not available with other types of golf balls. However, balata is easily damaged in normal play, and, thus, lacks the durability required by the average golfer.
In contrast, amateur golfers typically prefer a solid, two-piece ball with an ionomer cover, which provides a combination of distance and durability. Because of the hard ionomer cover, these balls are almost impossible to cut. They also have a very hard "feel", however, which many golfers find unacceptable, and a lower spin rate, making these balls more difficult to draw or fade. The reduction in the spin rate can be attributed to the differences between three-piece, wound golf balls and solid, two-piece balls in the composition and construction of both the cover and the core.
Many attempts have been made to produce a golf ball with the control and feel of a wound balata ball and the durability of a solid, two-piece ball, but none have succeeded totally. For example, U.S. Pat. No. 4,274,637 to Molitor discloses two- and three-piece golf balls having covers completely or partially formed from a cellular polymeric material to improve backspin, but does not provide any examples that compare the spin rates of the disclosed golf balls with those of prior art balls.
U.S. Pat. No. 5,002,281 to Nakahara et al. discloses a three-piece solid golf ball having an ionomer cover and a solid core consisting of a soft inner core and a hard outer shell, where the difference in the hardness of the two parts of the core is at least 10 on the JIS-C scale.
Similarly, U.S. Pat. No. 4,781,383 discloses a solid, three-piece golf ball, having an ionomer cover and a core with inner and outer layers, where the inner layer has a diameter of 24 to 29 mm and a Shore D hardness of 15 to 30, and the outer layer has a diameter of 36 to 41 and a Shore D hardness of 55 to 65. The percentage of the ball surface which contacts the club face when the ball is struck is 27 to 35%.
European Patent Application 0 633 043 discloses a solid, three-piece golf ball with an ionomer or balata cover, a center core, and an intermediate layer. The center core has a diameter of at least 29 mm and a specific gravity of less than 1.4. The intermediate layer has a thickness of at least 1 mm, a specific gravity of less than 1.2, and a hardness of at least 85 on the JIS-C scale.
U.S. Pat. Nos. 5,703,166 and 5,824,746 to Rajagopalan et al. and Harris et al. disclose golf balls incorporating blends of ionomers and non-ionic polyolefin polymers produced by metallocene catalysts. Metallocene catalysts are transition metal complexes that have substituted or unsubstituted cyclopentadienyl groups serving as ligands. The polymers produced using metallocene catalysts have a narrow molecular weight distribution, and a uniform molecular architecture, such that the order and orientation of the monomers in the polymer, and the amount and type of branching is essentially the same in each polymer chain. However, metallocene catalysts technology is limited to the production of non-polar polymers. Single-site catalysts other than metallocenes, such as those disclosed herein, can produce both polar and non-polar polymers with unique properties, which will have a dramatic influence in golf ball performance.
A number of single-site catalysts other than metallocenes are known. Recent articles have disclosed several non-metallocene single-site catalysts. The Apr. 13, 1998 issue of Chemical and Engineering News describes a method a producing complexes of iron (II) and cobalt (II) with 2,6 bis-(imino)pyridyl ligands. These single-site catalysts reportedly produce polymers with narrow molecular weight distributions, and a uniform molecular architecture.
Similarly, Brookhart et al., at the Sixth International Business Forum on Specialty Polyolefins, September, 1996, reported a class of nickel (II) and palladium (II) complexes which serve as active catalysts for the polymerization of ethylene and .alpha.-olefins. These complexes feature a substituted .alpha.-diimine ligand. Brookhart reports that by varying, among other things, the catalyst structure the degree and type of polymer branching can be controlled.
Cribbs et al., Antec, 1998, S.P.E., discloses several single-site catalysts other than metallocene. These include diimide complexes of nickel and palladium, and complexes of 1,4,7-triazacyclononane with rhodium, chromium, and scandium. Cribbs also discloses a process for forming non-metallocene single-site catalysts that consists of deprotonating pyroles or indoles to form a monoanion, and then reacting the monoanion with TiCl.sub.4 or ZrCl.sub.4 to form the single-site catalysts. This catalyst, when co-catalyzed with a sizable excess of methylalumoxane, has been found to polymerize ethylene to narrow molecular weight distribution polyethylene. Cribbs also discloses boratabenzene complexes of the Group 4 or 5 metals, and reports that these complexes show good activity in ethylene polymerization and that the molecular weights of the product can be varied by changing the substituents on the boron atom.
In the December 1997 issue of Chemtech, Montagna discloses several examples of non-metallocene single-site catalysts, including the Brookhart catalyst and the McConville catalyst, which is a zirconium complex stabilized by diamide ligands.
International patent application PCT WO96/23010 discloses several additional single-site catalysts. These include transition metal complexes, typically nickel or palladium complexes, having an .alpha.-diimine ligand.
However, although single-site catalysts are known, there is no known prior art disclosure of golf balls that incorporate compositions comprising polymers produced by such single-site catalysts, other than those produced using metallocene catalysts. Therefore, there is no appreciation in the prior art of the unique advantages obtained with golf balls produced with these materials.
While a variety of blend combinations of one species of polymer, such as ionomers, have been successfully used to make golf balls in the prior art, the prior art does not disclose successful blends of different types of polymers, such as ionomers and balata or other non-ionic polymers for use in golf ball covers. In general, prior art blends of such polymer components are immiscible, i.e., heterogeneous on a microscopic scale, and incompatible, i.e., heterogeneous on a macroscopic scale, unless strong interactions are present between the polymer components in the mixture, such as those observed between ionomers and polymers containing carboxylic acid groups. In particular, this lack of compatibility exists when an ionomer is blended with a polyolefin homopolymer, copolymer, or terpolymer that does not contain ionic, acidic, basic, or other polar pendant groups, and is not produced with a single-site catalyst. These mixtures often have poor tensile strength, impact strength, and the like. Hence, the golf balls produced from these incompatible mixtures will have inferior golf ball properties such as poor durability, cut resistance, and so on. In contrast, a compatible blend may be heterogeneous on a microscopic scale, but homogeneous on a macroscopic scale, and, thus, have useful golf ball properties.
In this regard, U.S. Pat. No. 5,397,840 to Sullivan discloses golf ball covers including a blend of "ionic copolymers" and "non-ionic copolymers". However, the "ionic copolymers" are defined as copolymers of an .alpha.-olefin and a metal salt of an .alpha.,.beta.-unsaturated carboxylic acid, and the "non-ionic copolymers" are copolymers or terpolymers containing ethylene or propylene and acrylic or methacrylic acid monomers. Therefore, strong interactions exist between the metal salts of the "ionic copolymers" and the acrylic or methacrylic acid monomers of the "non-ionic copolymers" that allow compatible blends to be formed. These interactions do not exist in prior art blends of ionomers and polymers that are truly non-ionic or non-polar, in particular, those polymers produced with a process that does not involve the use of a single-site catalysts.
U.S. Pat. Nos. 4,986,545; 5,098,105; 5,187,013; 5,330,837; and 5,338,610 to Sullivan disclose golf balls having covers comprising blends of ionomers and modified thermoplastic elastomers, where the thermoplastic elastomers are conventional polymers, i.e., polymers polymerized using catalysts other than single-site catalysts. The modified polymers include maleic anhydride modified ethylene-propylene copolymers, maleic anhydride modified styrenic block copolymers, maleic anhydride modified ethylene-vinyl acetate copolymers, brominated styrene-isobutylene copolymers, amine modified ethylene-propylene rubber, and polar modified paramethylstyrene-isobutylene copolymers. However, Sullivan does not exemplify blends of ionomers with any type of modified polyolefin, including those produced with single-site catalysts. Although the disclosed balls are said to exhibit enhanced playability, i.e., softness and spin, without sacrificing coefficient of restitution and, thus, carrying distance, all of the exemplified balls have a Riehle Compression in the range of 61 to 43, which corresponds to a PGA Compression range of from 99 to 117. Therefore, even though the disclosed cover materials may be relatively soft, each of the disclosed balls has an extremely high compression, and, thus, would be expected to have a high coefficient of restitution.
As shown in U.S. Pat. No. 5,703,166, metallocene catalyzed polymers and ionomers form compatible blends having useful golf ball properties. Co-pending application No. 08/950,197 discloses golf balls comprising grafted metallocene catalyzed polymers. However, there is no known prior art disclosure of golf balls incorporating compositions comprising grafted non-metallocene single-site catalyzed polymers.
Single-site catalyzed polymers, such as those mentioned above, may be functionalized by grafting functional groups onto the polymer chain. Processes for grafting monomers onto polymers, in particular, polyolefins, are known. European Patent Application No. 0 266 994 of P. C. Wong discloses a process for grafting ethylenically unsaturated monomers, such as unsaturated carboxylic acids and anhydrides and derivatives thereof, onto copolymers of ethylene. The disclosed process comprises the steps of forming an admixture of the copolymer, the monomer, and 25 to 3,000 ppm of an organic peroxide having a half-life of from about one minute to about 120 minutes at 150.degree. C., and mixing the resultant admixture in an extruder at a temperature above the melting point of the copolymer for a time at least four times the half-life of the organic peroxide. The resultant grafted copolymer is then extruded into a shaped article.
U.S. Pat. No. 5,106,916 to Mitchell discloses a process for the catalytic grafting of an ethylenically unsaturated monomer onto a copolymer in which the process of EPA 0 266 994 is modified by the addition of a catalyst comprising water and at least one phosphorous-containing compound selected from the group consisting of compounds of formula HPO(OR.sub.1).sub.2, phosphite compounds of formula P(OR.sub.2).sub.3 and formula (OR.sub.3)P--O--R.sub.4 --O--P(OR.sub.5).sub.2, and disubstituted pentaerythritol diphosphites of formula (R.sub.6 O)P--O.sub.2 --R.sub.PE O.sub.2 --P(OR.sub.7), where O.sub.2 R.sub.PE O.sub.2 is the pentaerythritol moiety, and R.sub.1 --R.sub.7 are specified organic functional groups.
Therefore, there is a need in the golf ball art for a golf ball formed of one or more compositions incorporating single-site catalyzed polymers, as well as blends of single-site catalyzed polymers with other polymers, including, but not limited to, ionomers. In particular, the inclusion of foamed and unfoamed, grafted or non-grafted, single-site catalyzed polymers, and blends of such polymers will allow highly durable golf balls to be produced with improved performance and virtually any combination of feel and spin rate.